With few exceptions, the hydrogenation of aliphatic dinitriles, NCRCN (I), is usually carried out to completion, i.e., with addition of 4 mol of hydrogen per mol of dinitrile, in order to prepare the corresponding diamines, H.sub.2 NCH.sub.2 RCH.sub.2 NH.sub.2 (II). These are used, among other applications, in production of various polyamides. Thus, for example, adiponitrile is hydrogenated to hexamethylenediamine, one of the two monomers required in the production of Nylon 6,6; methylglutaronitrile is hydrogenated to methylpentamethylenediamine and/or 3-methylpiperidine; and dodecanedinitrile is hydrogenated to dodecamethylenediamine.
The preparation of linear aminonitriles by hydrogenation of the corresponding dinitriles is known. U.S. Pat. Nos. 2,208,598 (1940) and 2,257,814 (1941) to Rigby of E.I. du Pont de Nemours and Co. disclose nickel-on alumina and cobalt-containing catalysts in liquid ammonia and teach away from the use of nickel as a catalyst.
A development by Swerdloff (U.S. Pat. No. 2,762,835 (1956)) carries out the essential reaction in a mixed organic solvent, such as methyal (i.e., dimethoxymethane), dioxane, tetrahydrofuran, or methyl cyclohexane, which is inert to hydrogen; the reaction is terminated after at least 40% and before more than 65% of the dinitrile originally present is reacted. A specified method of practicing the invention involves using a hydrogenation catalyst of the ferrous metal group. An organic solvent is used and the reaction is conducted in the presence of anhydrous ammonia. Unreacted dinitrile must be distilled or extracted from the aminonitrile.
The use of Raney nickel and Group VIII metal catalysts in solvents such as benzene and toluene are disclosed in German Pats. 836,938 (1952) and 848,654 (1952), both issued to BASF.
Selectivity to aminonitriles can be achieved using Rh/MgO catalyst, as disclosed in U.S. Pat. Nos. 4,389,348 (1983) and 4,601,859 (1986), both to Allied Corporation, and in a paper "Preparation and Characterization of a Novel Catalyst for the Hydrogenation of Dinitriles to Aminonitriles", F. Mares, J. E. Galle, S. E. Diamond, and F. J. Regina, J. Catl. 112:145-156 (1988). However, the high price of rhodium makes this approach expensive.
The preparation of branched aminonitriles by hydrogenation of the corresponding dinitriles is described in U.S. Pat. No. 3,322,815(1967) and Belg. Pat. No. 681.932 (1966) both issued to National Distillers. These disclose the preparation of 5-amino-2-methylvaleronitrile using a nickel, cobalt, or ruthenium metal catalyst, liquid ammonia or a tertiary alkyl amine and an alkanol solvent. The latter patent describes a two-step process from compounds such as 2-methyleneglutaronitrile.